Your Fertility: Understanding Natural Conception
Estradiol is responsible for stimulating other events to occur, all of which will result in optimal chances of the egg being fertilized and a pregnancy resulting. For example, estradiol is responsible for the changes in the cervical mucus. During much of the cycle, the cervical mucus is an impenetrable barrier, protecting the uterus and tubes from bacteria and anything else, including sperm. At about the time the egg is mature and ready to be released, the cervical mucus changes as a result of the ever-increasing amounts of estradiol being produced by the follicle. The mucus becomes thin and watery, and rather than preventing sperm from entering the uterus, it actually enhances this activity for a couple of days (but only right around the time of ovulation).
Estradiol is also responsible for the development of the lining of the uterus (the endometrium). All of these events occur in synchrony so that on day 14 of the ideal 28-day cycle, ovulation occurs, the cervical mucus is penetrable, and the lining of the uterus is getting ready to accept an implantation.
Intercourse must occur reasonably near the time of ovulation. Shortly after ovulation, the cervical mucus again becomes too thick for the sperm to penetrate; too long before ovulation, the sperm simply will not survive long enough to fertilize the egg. Having intercourse every other day around the time of ovulation is probably optimal. If, for example, a couple has intercourse every other day (days 10, 12, 14, and 16 in a 28-day cycle), they have done all they can do—at least in terms of enhancing their chances of pregnancy. More frequent intercourse does not further improve the chances of pregnancy as there begins to be a decrease in the number of sperm available if intercourse occurs more frequently than once every 48 hours.
It is possible to predict ovulation, and thereby time intercourse. Ovulation is preceded by a surge, or rapid increase, of a hormone called LH (luteinizing hormone). This surge can be detected through the use of an ovulation predictor, which is an over-the-counter test sold in any drug store. There are many ovulation predictors available, but they all function by detecting an increase in the amount of LH in the urine. They are really quite reliable and may be of value in timing intercourse. When the ovulation predictor changes, suggesting imminent ovulation, it is time to have intercourse.